CVE-2020-5284: Zeit Next.js Path Traversal Vulnerability

CVE-2020-5284 Overview

CVE-2020-5284 is a directory traversal vulnerability affecting Next.js versions prior to 9.3.2. Attackers can craft specially formatted HTTP requests to access files within the .next distribution directory, potentially exposing build assets and sensitive configuration data. While the vulnerability is limited to the .next directory and does not permit access to files outside this scope, applications that store sensitive assets in this directory may be at risk of information disclosure.

Critical Impact

Unauthorized access to build assets and potentially sensitive application data stored in the .next distribution directory through crafted path traversal requests.

Affected Products

• Zeit Next.js versions prior to 9.3.2
• Applications using vulnerable Next.js versions with sensitive data in the .next directory
• Deployments where the .next directory contains custom assets or configuration files

Discovery Timeline

• 2020-03-30 - CVE-2020-5284 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-5284

Vulnerability Analysis

This directory traversal vulnerability (CWE-22, CWE-23) exists in the request handling logic of Next.js. The framework fails to properly sanitize user-supplied path components in HTTP requests, allowing attackers to navigate outside the intended web root into the .next distribution directory. This directory typically contains compiled JavaScript bundles, server-side rendering artifacts, and cached build data.

The impact is primarily information disclosure. While the vulnerability's scope is limited to the .next directory, exposure of build artifacts could reveal application logic, API endpoints, environment-specific configurations, or other sensitive implementation details that could aid further attacks.

Root Cause

The vulnerability stems from insufficient input validation and path canonicalization in Next.js's static file serving mechanism. When processing requests for static assets, the application fails to properly validate and normalize path components, allowing sequences like ../ to traverse directories within the constraints of the .next folder.

Attack Vector

The attack is network-based and requires low privileges to execute. An attacker sends crafted HTTP requests containing directory traversal sequences targeting the .next distribution folder. The server processes these malicious paths without adequate sanitization, returning file contents from within the distribution directory.

The exploitation mechanism involves manipulating URL path components to escape the intended static file serving boundaries. Attackers typically inject encoded or literal ../ sequences to navigate the directory structure and access build artifacts that should not be publicly accessible.

Detection Methods for CVE-2020-5284

Indicators of Compromise

• HTTP access logs showing requests with encoded or literal ../ sequences targeting .next paths
• Unusual access patterns to build artifact files (e.g., .next/server/, .next/static/)
• Requests containing URL-encoded traversal characters (%2e%2e%2f, %2e%2e/)
• Web application firewall (WAF) alerts for path traversal attempt signatures

Detection Strategies

• Implement WAF rules to detect and block common directory traversal patterns in request URLs
• Configure intrusion detection systems (IDS) to alert on path manipulation attempts targeting Node.js applications
• Enable verbose request logging and monitor for anomalous access to .next directory contents
• Deploy runtime application self-protection (RASP) solutions to identify traversal attempts in real-time

Monitoring Recommendations

• Monitor web server access logs for requests containing path traversal sequences
• Set up alerts for unexpected file access within the .next distribution directory
• Review application logs for error messages related to file path resolution
• Implement file integrity monitoring on sensitive build artifacts

How to Mitigate CVE-2020-5284

Immediate Actions Required

• Upgrade Next.js to version 9.3.2 or later immediately
• Audit your .next directory for any sensitive files that may have been intentionally or unintentionally stored there
• Review access logs for evidence of exploitation attempts
• Implement WAF rules to block path traversal patterns as a defense-in-depth measure

Patch Information

The vulnerability has been addressed in Next.js version 9.3.2. Organizations should upgrade to this version or later to remediate the vulnerability. Detailed release information is available in the GitHub Next.js Release v9.3.2. Additional technical details about the vulnerability can be found in the GitHub Security Advisory GHSA-fq77-7p7r-83rj.

Workarounds

• Configure reverse proxy or web server rules to block requests containing directory traversal sequences
• Implement network-level access controls to restrict direct access to application servers
• Remove or relocate any sensitive files from the .next distribution directory
• Deploy a WAF with path traversal detection capabilities in front of affected applications

# Example nginx configuration to block path traversal attempts
location / {
    # Block requests containing directory traversal sequences
    if ($request_uri ~* "\.\.") {
        return 403;
    }
    
    # Block direct access to .next directory
    location ~ /\.next {
        deny all;
        return 404;
    }
    
    proxy_pass http://nextjs_backend;
}